System for controlling air-fuel ratio

Abstract

A system for controlling the air-fuel ratio for an internal combustion engine having an intake passage, an exhaust passage, a detector such as an oxygen sensor for detecting the concentration of oxygen in the exhaust gases, an air-fuel mixture supply unit, an on-off type electromagnetic valve for correcting the air-fuel ratio of the air-fuel mixture supplied by the air-fuel mixture supply unit, and an electronic control circuit for producing square wave pulses in dependency on the output signal from the detector for driving the on-off type electromagnetic valve. The system comprises a venturi for producing a vacuum dependent on rapid acceleration, a vacuum sensor for sensing the vacuum in the venturi at rapid acceleration of the internal combustion engine and producing an output signal dependent thereon, an intake opening in the venturi for communicating the vacuum with said vacuum sensor, pulse width modulator for producing a pulse width modulating signal when an output signal of the vacuum sensor rises above a predetermined level at a rapid acceleration, the pulse width modulator being connected to the electronic control circuit, such that said pulse width modulating signal is fed to said electronic control circuit for modulating the width of said square wave pulses in dependency on the rapid acceleration for enriching the air-fuel mixture.

What is claimed is: 
     
       1. In a system for controlling the air-fuel ratio for an internal combustion engine having a carburetor with an intake passage, air-fuel mixture supply means for supplying an air-fuel mixture to the intake passage, an exhaust passage communicating with the engine, a throttle valve in the intake passage, detecting means for detecting the concentration of a constituent of exhaust gases passing through said exhaust passage and providing an output signal dependent thereon, an electronic control circuit means for producing square wave pulses in dependency on said output signal of said detecting means, and an on-off type electromagnetic valve means actuated by the square wave pulses from said electronic control circuit means for correcting the air-fuel ratio of the air-fuel mixture supply means, the improvement comprising a venturi means in the intake passage upstream of said throttle valve for producing vacuum dependent on rapid acceleration of said internal combustion engine,   a vacuum sensor means for sensing said vacuum in said venturi means at rapid acceleration of the internal combustion engine and for producing a second output signal dependent thereon,   pulse width modulating means for producing a pulse width modulating signal when the second output signal of said vacuum sensor means rises above a predetermined level at rapid acceleration,   said pulse width modulating means being connected to said electronic control circuit means for feeding said pulse width modulating signal to said electronic control circuit means for modulating the width of said square wave pulses in dependency on said rapid acceleration for enriching the air-fuel mixture.   
     
     
       2. The system for controlling the air-fuel ratio for an internal combustion engine according to claim 1 wherein said vacuum sensor means is for producing said second output signal changing in dependency on the magnitude of the rapid acceleration.   
     
     
       3. The system for controlling the air-fuel ratio for an internal combustion engine according to claim 1 further comprising intake opening means provided in said venturi means for introducing said vacuum to said vacuum sensor means,   said vacuum sensor means is responsive to the vacuum in the venturi means above a predetermined value.   
     
     
       4. The system according to claim 1 wherein said vacuum sensor means comprises a diaphragm means defining a chamber communicating with said venturi means and a potentiometer movably connected to said diaphragm means.   
     
     
       5. The system according to claim 1 wherein said pulse width modulating means includes a fixed duty ratio voltage source, a one pulse generating circuit connected to said vacuum sensor means and a small width pulse generating circuit means connected to an output of said one pulse generating circuit,   said electronic control circuit means includes an integration circuit connected to said pulse width modulating circuit and a comparing circuit connected to said detecting means and to said integration circuit, and a driving circuit means for driving the on-off type electromagnet valve means, a comparator operatively connected to an output of said integration circuit and to said driving circuit means and a standard triangular wave pulse generator connected to an input of said comparator,   a first switching means is connected between said output of said integration circuit and another input of said comparator,   a second switching means is connected between said fixed duty ratio voltage source and said another input of said comparator,   said small width pulse generating circuit means has an output connected to switching gates of said first and second switching means for generating a small width pulse upon receiving a pulse signal from said one pulse generating circuit for switching said first and second switching means during said rapid acceleration when the output voltage of the vacuum sensor means exceeds the predetermined level such that said first switching means opens and said second switching means closes during said small width pulse and vice versa otherwise, said small width pulse signal and said pulse signal constituting said pulse width modulating signal.   
     
     
       6. The system according to claim 5, further comprising third switching means disposed between said comparing means and said integration circuit and a fourth switching means disposed in said integration circuit and comprising means for increasing the gain in said integration circuit upon receiving said pulse signal from said one pulse generating circuit during said rapid acceleration when the output voltage of said vacuum sensor means exceeds the predetermined level.   
     
     
       7. The system according to claim 6, wherein said integration circuit includes a fifth switching means connected to the output of said small width pulse generating circuit for closing said fifth switching means and converting said integration circuit into an ordinary operational amplifier when said first switching means opens and said second switching means closes by said small width pulse.   
     
     
       8. The system according to claim 1, wherein said pulse width modulating means is for increasing the pulse width modulating signal with increasing vacuum.   
     
     
       9. In a method for controlling the air-fuel ratio for an internal combustion engine having a carburetor with an intake passage, air-fuel mixture supply means for supplying an air-fuel mixture to the intake passage, an exhaust passage communicating with the engine, a throttle valve in the intake passage, detecting means for detecting the concentration of a constituent of exhaust gases passing through said exhaust passage and producing an output signal dependent thereon, an electronic control circuit means for producing square wave pulses in dependency on said output signal of said detecting means, and an on-off type electromagnetic valve means actuated by the square wave pulses from said electronic control circuit means for correcting the air-fuel ratio of the air-fuel mixture supplied by said air-fuel mixture supply means, the improvement comprising producing a vacuum dependent on a rapid acceleration of the engine in a venturi in the intake passage upstream of the throttle valve and detecting the vacuum and producing a second output signal dependent thereon,   producing a pulse width modulating signal when the second output signal rises above a predetermined level upon rapid acceleration, and   modulating the width of said square wave pulses by the pulse width modulating signal in dependency on said rapid acceleration for enriching the air-fuel mixture.